In general, a nitride semiconductor material has been widely used in a green or blue light emitting diode (LED) or in a laser diode provided as a light source in a full-color display, an image scanner, various signaling systems, or in an optical communications device. A nitride semiconductor light emitting device may be provided as a light emitting device having an active layer emitting light of various colors, including blue and green, through the recombination of electrons and holes.
As remarkable progress has been made in the area of nitride semiconductor light emitting devices since they were first developed, the utilization thereof has been greatly expanded and research into utilizing semiconductor light emitting devices as light sources of general illumination devices and electronic devices, has been actively undertaken. In particular, related art nitride light emitting devices have largely been used as components of low-current/low-output mobile products, and recently, the utilization of nitride light emitting devices has extended into the field of high-current/high-output devices. Thus, research into improving luminance efficiency and the quality of semiconductor light emitting devices has been actively conducted.
In terms of the luminance efficiency of a semiconductor light emitting device, light generated from an active layer is trapped and lost in the interior of semiconductor due to total internal reflection caused by a difference between refractive indices of air and the semiconductor layer, degrading light extraction efficiency. For example, GaN has a refractive index of about 2.5, and only about 4% of light made incident at 23° due to a difference between the refractive index of GaN and the refractive index (about 1) of air can escape to the outside. Thus, in order to minimize such light loss, research into enhancing light extraction efficiency by forming depressions and protrusions on a GaN surface has been ongoing.
Thus, a need exists for further improvement, for example, in terms of enhanced light extraction efficiency, optical power and luminous intensity uniformity in semiconductor light emitting devices.